CardName: Temple of Fire
Cost:
Type: Land - Temple
Pow/Tgh: /
Rules Text: Temple of Fire enters the battlefield under the control of
an opponent of your choice.
{T}: Add {r} to your mana pool.
Whenever a creature controlled by Temple of Fire's owner
deals 3 or more damage to you, that player gains control of
Temple of Fire and transforms it.
Flavour Text:
Back side:
CardName: Megaton Hammer
Cost:
Type: Artifact - Equipment
Pow/Tgh: /
Rules Text: Equipped creature gets +3/+0 and has trample.
{1}, {T}: Tap target artifact or creature.
Equip {2}
Flavour Text:
Set/Rarity: A Link to the Coast Rare
Temple of Fire
R
Land – Temple
Temple of Fire enters the battlefield under the control of an opponent of your choice.
: Add to your mana pool.
Whenever a creature controlled by Temple of Fire's owner deals 3 or more damage to you, that player gains control of Temple of Fire and transforms it.
Megaton Hammer
R
Artifact – Equipment
Equipped creature gets +3/+0 and has trample.
, : Tap target artifact or creature.
Equip
: Add 
to your mana pool.
, 
This is a bad design for many reasons, but maybe it will inspire someone else to make a better design.
Why not just have quest lands? Reverse-XLN lands that transform into something if you meet certain criteria.